The present invention generally relates to a cardiac stimulation system. The invention more particularly relates to such a system which includes and provides performance evaluation of an implantable cardiac stimulation device for determining if the implanted device is performing as expected.
Implantable cardiac stimulation devices are well known in the art. They include implantable pacemakers which provide stimulation pulses to a heart to cause a heart, which would normally or otherwise beat too slowly or at an irregular rate, to beat at a controlled normal rate. They also include defibrillators which detect when the atria and/or the ventricles of the heart are in fibrillation and apply cardioverting or defibrillating electrical energy to the heart to restore the heart to a normal rhythm. Implantable cardiac stimulation devices may also include the combined functionalities of a pacemaker and a defibrillator.
As is well known, implantable cardiac stimulation devices sense cardiac activity for monitoring the cardiac condition of the patient in which the device is implanted. By sensing the cardiac activity of the patient, the device is able to provide cardiac stimulation therapy when it is required.
When an implantable cardiac stimulation device is implanted in a patient, it is typically implanted to correct a symptom or problem which the patient is experiencing. Modern implantable devices include a telemetry circuit to permit them to be programmed by external devices, such as programmers, to best fit the needs of the patient. The device is thereafter checked periodically to ensure that the device is interacting with the patient""s heart as intended and, hence, is performing as intended. If the device is not performing as intended or needed, its operation is then adjusted through programming to adjust the programmable parameters of the device.
The medical personnel performing the follow-up check is commonly not the same person who prescribed, implanted and initially programmed the device. Hence, the person performing the follow-up check may not be fully aware of the intended device performance for that patient. Further, even if the same person performs the follow-up check, that person may not recall the intended device performance details for that patient. As a result, the person responsible for the follow-up check will not know what the intended device performance is and, hence, if the device is performing as intended.
The follow-up process traditionally requires the making of judgements based upon observations of several characteristics of the patient with the implanted device. For example, this may include the taking of telemetered ECG recordings, programmed settings (i.e., mode, rate, refractory period, pulse amplitudes and pulse width, etc.), measured data (i.e., battery voltage, current and impedance, lead impedances, etc.) and performance data recorded by the device over at last prior recording period (i.e., patient paced and sensed, heart rate histograms, sensor rate histograms, etc.) which indicate the interaction of the patient with the implanted device. In addition, some implantable devices may provide telemetered notes made by the physician about the disease diagnosis for the patient, the purpose for the device implant and device component types and implant locations.
Even with the above mentioned wealth of information which may be provided to the follow-up medical personnel by modern day implantable cardiac devices, there still remains the problem of knowing what the intended device performance is and hence if the device is performing as intended for the patient. This problem will only become more difficult as future implantable devices provide even more programmability and types and quantity of diagnostic data.
The present invention provides an implantable cardiac stimulation system and method wherein the implanting physician may store, in the system, parameters which define the expected performance of the device in conjunction with the programming of the device to address the needs of the patient. The person performing follow-up testing of the device and its interaction with the patient may, with an external programmer, be advised of the expected performance of the device at follow-up.
In accordance with the present invention, the implanted device generates performance data indicative of the interaction between the device and the patient""s heart, e.g., paced and sensed heart rate histograms, sensor rate histograms, etc. Performance limits, defining the expected interaction of the device and the patient""s heart associated with the generated performance data are established and stored, either in the implantable device or in the external programmer. After implant, the generated performance data is evaluated to determine if the generated data satisfies the established performance limits and the evaluation results are reported.
In accordance with the present invention, the generated performance data may be stored in histogram format and the limits may be expressed as percents or ratios. The data and limits may relate to heart rate, rhythms, sensor rates, etc.
The limits may be stored either in the implantable device or an external device, such as a programmer. Similarly, the data evaluation may be performed by either the implantable device or the external device.
The reporting of the evaluation results may include reporting out of limit conditions, within limit conditions, the limits, and/or the generated data.
In accordance with a further aspect of the present invention, when the evaluation reveals that the generated data satisfies the established limits, the limits may be revised to facilitate future follow-up. The limit revisions may be based upon the generated data. Preferably, the generated data is used to establish a baseline and the limits are revised based upon the baseline.
The implantable device and the external device preferably include telemetry circuitry to facilitate interaction between the implanted device and the external device. The telemetry may be utilized for conveying the generated data, the limits and/or the evaluation results to the external device for analysis and/or display.